1. Field of the Invention
The present invention relates to a magnetic head assembly used in a linear recording magnetic tape apparatus. More specifically, the present invention relates to a magnetic head assembly using a magnetic resistance element of a magnetic resistance (MR) type, a giant magnetic resistance (GMR) type, a tunneling junction magnetic resistance (TMR) type, or the like. The present invention also relates to a magnetic tape apparatus using such a magnetic head assembly.
2. Description of Related Art
In the field of a magnetic tape for data backup, a magnetic tape having a recording capacity of 800 GB or more per volume has been commercialized along with the increase in capacity of a hard disk targeted for backup. Furthermore, a large-capacity future backup tape having a capacity exceeding 4 TB has been proposed, and the increase in capacity thereof is indispensable.
A recording/reproducing magnetic head assembly used in such a large-capacity magnetic tape apparatus includes an induction head element (recording element) capable of recording information on a magnetic tape and an MR induction complex head element (reproducing element) capable of reading information recorded on the magnetic tape. The induction head element is configured by forming a magnetic pole, a coil, a MR element layer, and the like on a base, using a thin film generation method. The MR induction complex head element can be formed of a MR head element. The magnetic head assembly is configured by placing a plurality of (for example, 8 to 16) induction head elements and MR induction complex head elements on a head rail that has an elongated shape in a direction orthogonal to a magnetic tape traveling direction. Generally, the magnetic head assembly has a configuration in which two head rails are arranged in parallel in the magnetic tape traveling direction. The number of head rails may be one or at least three.
In the magnetic head assembly with such a configuration, during traveling of a magnetic tape in a forward direction, a signal is recorded on the magnetic tape with magnetic heads mounted on a leading rail, and a signal recorded on the magnetic tape is reproduced with magnetic heads mounted on a trailing rail. Such an operation is performed for simultaneous recording and reproduction in a plurality of channels (8 to 16). Furthermore, during traveling in a reverse direction, an operation opposite to the above operation during traveling in a forward direction is performed. Herein, a magnetic head assembly, in which a rail without head chips is present, may be used.
Furthermore, in these magnetic head assemblies, a servo head (MR head chips for reproducing a servo signal) is provided at each end of a head rail with a plurality of recording elements and reproducing elements mounted thereon. The servo head can read a servo signal recorded on a magnetic tape. The magnetic tape apparatus controls the position of the magnetic head assembly in a tape width direction so that magnetic heads can trace a predetermined track, based on the servo signal read by the servo head. There also is a magnetic tape apparatus that reads a servo pattern, which has a plurality of concave portions for detecting an optical position and is formed on a backcoat side of a magnetic tape, with an optical sensor, thereby performing tracking servo.
FIG. 4A shows an example of a magnetic head assembly composed of four rails. FIG. 4B shows a cross-section taken along a Z-Z line in FIG. 4A. As shown in FIGS. 4A and 4B, in a magnetic head assembly 101, a pair of head chip groups 103a and 103b are placed in a part of four rails 102 on which a magnetic tape slides. As shown in a Y-portion (enlarged view of the head chip group) in FIG. 4A, one head chip group is composed of a data head 110 including 16 head chips capable of recording or reproducing a data signal with respect to a magnetic tape, and a servo head 111 placed at each end of the data head 110, capable of reading a servo signal recorded on the magnetic tape.
FIGS. 5A and 5B show a configuration of one magnetic head (a part of the data head 110) in the head chip group shown in FIG. 4A. FIG. 5A is a plan view of the magnetic head. FIG. 5B is a cross-sectional view taken along an X-X line in FIG. 5A. The magnetic head includes a base 1, an insulating layer 2, a magnetic shield layer 3, a MR element 4, a magnetic shield layer 5, a magnetic pole layer 6, a gap portion 7, a magnetic pole layer 8, a conductive coil 9, and a base 11. Ahead element portion includes the magnetic shield layer 3, the MR element 4, the magnetic shield layer 5, the magnetic pole layer 6, the gap portion 7, the magnetic pole layer 8, and the conductive coil 9.
In FIG. 5B, a dimension d1 corresponds to an initial pole tip recession (PTR). Furthermore, the dimension d1 is a depth of a concave portion 13 (abrasion level difference) caused by the difference in abrasion characteristics between the bases (AlTiC) 1 and 11, and the insulating layer (alumina glass) 2 and the head element portion (various kinds of materials) in a final polishing step in the course of production of the magnetic head assembly.
In a conventional linear magnetic head assembly, as shown in FIG. 5B, the surface of the head rail 102 including the surfaces of the bases (sliding portions) 1, 11 and the head element portion, opposed to the magnetic tape, is not provided with a protective film or the like, and the magnetic tape slides directly on the surface of the head rail 102. Document 1 (JP 7-230615 A) discloses a configuration in which a protective film such as a silicon oxide film or a carbon film is formed by sputtering only in a level difference caused by a treatment, generated in the head element portion in a thin film magnetic head for a hard disk.
In a conventional thin film magnetic head, stain (brown stain) adheres to the sliding surface between the head element portion and the magnetic tape, particularly, under a condition that recording and reproduction are performed repeatedly with respect to the same magnetic tape in a low humidity environment (20° C., 10% RH), which increases spacing. When the spacing increases, there arises a problem in that a reproduction output decreases, and an error rate increases. The stain is caused when a surface layer component of a magnetic layer of a magnetic tape peels off during traveling of the magnetic tape and adheres to the surface of the head element portion. It is conceivable that the stain adheres to the surface of the head element portion due to the heat generation caused by a current applied to the magnetic head during recording and reproduction, and the thermoelectric chemical reaction in which a potential difference occurs between the base (AlTiC) and the head chip due to the friction during traveling of the magnetic tape. Regarding the relationship between the potential difference between the base and the head chip, and the stain, research as described in Document 2 (Center for Magnetic Recording Research (CMRR) Report, page 11, number 24, Summer 2005, University of California, San Diego) has been conducted.
In the case of the magnetic head for a magnetic disk as disclosed by Document 1, a minute magnetic head slider (magnetic head assembly) placed at the end of a gimbal opposed to a magnetic disk is kept in contact with the magnetic disk during the suspension of the rotation of the magnetic disk When the magnetic disk is rotated at a high speed, the magnetic head slider floats from the magnetic disk due to the air bearing effect caused by the relative movement between the head rail and the magnetic disk according to a contact start stop (CSS) system. In contrast, the magnetic head for a magnetic tape comes into contact with a magnetic tape even during traveling of the magnetic tape. Furthermore, the stiffness of a medium in the magnetic disk is very high, so that the difference in hardness between the magnetic disk and the magnetic head is not so large. The magnetic tape is very thin and has low stiffness, so that the difference in hardness between the magnetic tape and the magnetic head is large.
As described above, in the case of the magnetic head for a magnetic tape, the PTR during traveling of the magnetic tape proceeds due to the aggressive abrasion. On the other hand, in the case of the magnetic head for a magnetic disk, a magnetic head assembly portion including a head element portion floats from the magnetic disk, so that the magnetic head assembly portion is almost in no-contact with the magnetic disk, and hence, polishing powder is not generated, and aggressive abrasion does not occur. However, according to the configuration in which a magnetic tape is allowed to travel while the magnetic tape is in contact with the magnetic head as in the magnetic head for a magnetic tape, the difference in hardness between the material for the magnetic tape and the material for the magnetic head is large, so that aggressive abrasion occurs to allow the PTR to proceed. The “aggressive abrasion” refers to the abrasion caused by the contact among three bodies. For example, the aggressive abrasion refers to the abrasion caused by the contact among three bodies: a magnetic head, a magnetic tape, and polishing powder (dropped substances from the magnetic tape, the magnetic head, or the like).
Furthermore, Document 1 discloses that a protective film is provided only in a concave portion of a head element portion of a magnetic head for a magnetic disk. According to this procedure, a protective film is not formed in a base portion, so that potential difference is likely to be caused between the base portion and the head element portion. Consequently, the generation of the above-mentioned stain cannot be prevented sufficiently.